The Effect of Surfactants on Equilibrium Wetting

Contact angles B0 of aqueous solutions contacting with hydrophilic and hydrophobic surfaces were studied as affected by various surfactants (alcohols, fatty acids, soaps) under conditions close to thermodynamic equilibrium (in the atmosphere saturated with the solution vapour). The conditions of transitions from limited wetting (Bo > 0) to complete wetting, i.e. spontaneous spreading were also studied. The effect of surfactants adsorption at the solid gas interface was estimated from the isotherms of wetting tension W = cr1g Cos B0 (cr1g is the surface tension of the solution) on the basis of equation describing W as a function of concentration. It is shown that adsorption of surfactants at the solid-gas interface markedly affects wetting of hydrophilic materials. For hydrophobic materials the effect is primarily due to adsorption of surfactants at the solid- solution and solution-gas interfaces. It was found that equilibrium wetting is affected by the type of adsorption at the solid surface (physical or chemical adsorption). The influence of hydrocarbon chain length in homological series of alcohols and fatty acids on equilibrium contact angles and on transition to spontaneous spreading was studied as well

Magnetic anisotropies of sputtered Fe films on MgO substrates

Ferromagnetic resonance (FMR) and superconducting quantum interference device (SQUID) measurements have been used to study the magnetic properties of rf sputtered Fe films on MgO(001) substrates. The dependences of the FMR spectra parameters on the direction of the dc magnetic field turning in the plane of the films were measured in a wide temperature range (20400 K) for films with thickness L in the range 25500. The analysis of the angular dependence of the resonance field H0 allowed us to determine the fourfold cubic anisotropy constant K1 and the effective magnetization value Meff. It was found that both values decrease with decreasing L and approach a constant value below a certain thickness. A theory of FMR is outlined demonstrating that for the case of the dc magnetic field lying in a film plane, the anisotropy constant can be interpreted as a combination of a volume anisotropy contribution and a 1/L-dependent contribution from the surface anisotropy up to the thickness L103. This means that for the experimentally studied thickness range the films may be considered as dynamically thin films with respect to surface perturbations. Then the peculiar thickness dependence of the K1 value can be explained assuming that the relaxation of the strain due to the mismatch between film and substrate extends to distances as far as 45 from the film-substrate interface. Since our SQUID measurements show that the saturation moment does not depend on the thickness, it is concluded that the thickness dependence of the effective magnetization Meff is caused by a second-order uniaxial anisotropy arising mainly from the broken symmetry of the crystal field at surfaces and near the edges of interfacial dislocations. © 1995 The American Physical Society

Structural variability of sunflower gene for methionine-rich albumin SFA8

Background. The 2S albumins of sunflower and other oilseed plants possess a high nutritional quality, the defense activity against fungi diseases casual gents and also valuable functional properties. The major component of albumin fraction, the SFA8 protein consists of 103 amino acid residues among which methionine constitutes 15 Mole %. In the cultivated sunflower gene pool the SFA8 structural gene is represented by the two alleles the products of which have different isoelectric points and differ by the electrophoretic mobility, however molecular mechanisms of the polymorphism are still unknown. Results. The amplified sequences of the SFA8 gene from seven Helianthus annuus L. accessions and three accessions of wild Helianthus L. species from VIR collection were sequences. The intron of 258-303 bp length depending on the genotype was firstly found in the central part of the gene. The length of the first exon constitutes 99 bp, the second exon is of 210 bp length. The nucleotide and translated amino acid sequences are polymorphic among different genotypes. The line VIR 130 in which the two expressing SFA8 proteins, the normal polypeptide with isoelectric point (pI) approximately 6.0 (normal SFA8) and its allelic variant with pI 6.5 (variant SFA8) have been earlier revealed possesses two types of the SFA8 encoding sequence. In one sequence the substitution 108С—G is present that results in the substitution of the polar uncharged amino acid serine for the positively charged arginine and respectively in alteration of the protein charge and isoelectric point. The intron sequence is also polymorphic and characterized by the presence of indels of approximately 45 bp. The intron sequences of all accessions contain dinucleotides GT at the 5΄ end and AG at the 3΄ end which are characteristic for consensus sequences of splicing sites in the U2-type introns. The variants of the secondary structure of the SFA8 intron sequences of H. argophyllus Torr. & A. Gray and all the analyzed H. annuus genotypes are similar and differ from those of H. petiolaris Nutt. and H. giganteus L. Conclusions. The data on the SFA8 gene sequence polymorphism are important understanding the molecular mechanisms of genotypic differences in biochemical and functional properties of the protein, and he revealed differences in the intron secondary structure can be important for understanding expression patterns of the protein

Hybrid subterahertz atmospheric pressure plasmatron for plasma chemical applications

This paper presents the results of an experimental study of a new hybrid plasmatron scheme, which was used to realize a gas discharge at atmospheric pressure supported by continuous focused submillimeter radiation with a frequency of 263 GHz. The implemented design allowed organizing a self-consistent interaction between submillimeter radiation and the supercritical plasma in a localized area both in terms of gas flow and electrodynamic. It is experimentally shown that the gas discharge absorbs up to 80% of the introduced submillimeter radiation power. The hybrid subterahertz plasmatron as an effective reactor for non-equilibrium plasma chemical processes was tested for the atmospheric nitrogen fixation

Possible origin for oscillatory superconducting transition temperature in superconductor/ferromagnet multilayers

We have studied superconducting and magnetic properties of sputtered Fe/Nb/Fe trilayers. For a fixed Nb thickness and with changing Fe thickness, dFe, a nonmonotonic behavior of the superconducting transition temperature Tc was observed with a maximum at dFe ≈ 10 Å. The analysis of the magnetization data revealed that for dFFe ≤7 Å the Fe layer is nonmagnetic. The interpretation of the observed Tc behavior is attributed to the existence of this magnetically "dead" layer and the change of the interaction of the Cooper pairs with this layer at the onset of ferromagnetism for dFe ≥ 7 Å

Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio